Electric timing control



Aug. 17, 1954 E. e. ANGER ELECTRIC TIMING CONTROL IN V EN TOR.

flTTaI/Y K Filed March 7, 1950 PatentedAug. 17, 1954 UNITED STATES PATENT OFFIE 2,686,872 ELECTRIC TIMING CONTROL Ernest G. Anger, Wauwatosa, Square D Company, Detroit,

tion of Michigan Application March 7,

8 Claims.

This invention relates to an electrical circuit employing capacitor-resistance timing of an operating period.

is small in comparison with the maximum resistance of the variable resistor, and large with respect to the minimum resistance of the variable resistor.

Another object of the present invention is a timing circuit in accordance with the preceding objects in which the capacitor discharges through the fixed and variable resistors, the voltage drop across the variable resistor determining the timing period.

Another object of the present invention is the provision of a timing circuit arrangement which utilizes a capacitor and a pair of serially connected resistors in parallel therewith, the circuit components and connections being such that the voltage between the control grid and cathode of the electronic tube is gradually dissipated, while the voltage applied to a second control element effects the actual initiating moment of conduction.

Other objects and features of the invention will be readily apparent to those skilled in the art from the specification and appended drawing illustrating certain preferred embodiments in which:

The figure is a diagrammatic representation of a welding circuit including the timing arrangement of applicants invention.

In the figure the numerals I and 2 represent a pair of main supply lines which are connected to a source of energy which is not illustrated. Connected across these lines I and 2 is a valve Wis., assignor to M1ch., a corpora.-

1950, Serial No. 148,191 (Cl. 25027) is connected between the conductors I and 8, to provide these conductors with a pulsating D. C. voltage.

serially disposed across the conductors i and 8 is a pair of resistors I3 and I4 which are connected by a conductor I5 to a timing circuit comprising a fixed resistor I6, a variable resistor I1 in series therewith, and a capacitor l8 connected in parallel with these two resistors.

This timing circuit is connected to the conductor I through a normally closed contact l9, and also to the control grid 2| of an electronic tube 22 having a cathode 23 and an Tube 22 has a shield grid 25 which is connected between a capacitor 26 and a resistor 27 serially disposed between the conductors 1 and 8.

Connected to the resistor 29 is a conductor 3| which serves to connect a timing circuit, comprising an adjustable resistor 32 and a capacitor 33 in series therewith, to the anode circuit of tube 22. The capacitor 33 is normally shorted out by a contact 34 which is normally closed. A conductor 35 is connected between the adjustable resistor 32 and the capacitor 33 and to a secondary 36 of a transformer 45, the primary of which is connected across lines I and 2, the secondary 36 serving to supply heat to the cathode 31 of an electronic tube 38. This tube has an anode 39 and a control grid 4| and the principal electrodes are supplied from a secondary 46 of the transformer 45. A capacitor 42 is connected between the control grid 4| and the cathode 31 of the tube 38, and to a point between a pair of voltage dividing resistors 43 and 44 which are serially disposed between the conductors I and 8. A relay coil 41 is disposed between the anode 39 of tube 38 and the transformer secondary 46, the relay coil 41 being parallel by a capacitor 48 and an inductor 49, this parallel circuit being further parallelled by the primary of a transformer 5!. The advantages and detailed operation of this relay circuit are particularly pointed out and claimed in applicants copending application entitled Electric Control Circuit, filed March '7, 1950, Serial No. 148,190, now Patent No. 2,634,320, granted April 7, 1953.

The relay coil 4? controls the closure of a normally open contact 52 connected in a back to-back circuit comprising ignitrons 53 and 54 conventionally disposed between the main'lines l and 2 and serving to control the energization of a welding transformer 55 having a secondary 5% for passing current to the work to be welded. The stroke of this relay is designed so that contact 52 closes during the first half cycle following the first conducting half cycle of tube 38, and in the preferred embodiment at a point in that half cycle which approximately corresponds to a normal current zero point for a welding transformer of average power factor. The secondary of transformer M is connected through a resistor to a control grid 51 of an electronic tube 58, the anode of which is connected to the conductor I, the cathode being connected to a timing circuit comprising a fixed resistor 59, an adjustable resistor 6! in series therewith, and a parallel capacitor 62, a conductor 63 being connected between the fixed and variable resistors to introduce a voltage into the timing circuit from a second circuit comprising a resistor 64 and resistor 65, these latter resistors being serially connected between the conductor '5 and a cathode heating circuit to be subsequently explained. The timing circuit arrangement consisting of capacitor 62 and resistors 59 and BI is like that described for the arrangement of capacitor l3 and resistors It and H.

The capacitor 52 is connected to a control grid 66 of an electronic tube 5! having an anode 68 and a cathode 69, the anode Eil'being connected through a resistor ll to the conductor 9 while the cathode 69 is connected to the aforementioned cathode heater circuit. The resistor H is connected through another resistor to a control grid 12 of an electronic tube 13, the anode of which is connected to the conductor 1, while the cathode is connected to another timing circuit comprising a fixed resistor M and a variable resistor '55 in series therewith, the series circuit being paralleled bygcapacitor Hi. The arrangementof this timing circuit is like that previously described. A voltage is introduced into this timing circuit by a conductor Hi from a series circuit comprising a resistor TH and a resistor 18 these resistors being serially disposed between conductor l and the aforementioned cathode heat circuit.

The capacitor T6 is connected to a control grid 19 of an electronic tube 8i, having an anode 82 and a cathode 83, these electrodes of tube 8i being connected across one secondary 34 of a transformer 85 through a normally open manual operated switch $36 and a relay coil Bl, a capacitor 88 paralleling the relay coil. The primary of transformer 85 is connected across the supply lines I and 2. The relay coil controls the operation of a contact 89, which is normally open and which parallels the manually operated switch 56, this relay coil also controlling the operation of contacts t, ill, 28 and 34. A second secondary st of transformer 85 supplies the cathode heaters of tubes 22, 6'! and 8!.

In the description of the circuit, conventional elements such as surge bypass capacitors, fuses, thermal flow switches and other conventional elements have been eliminated although these would be present in an operating circuit. This elimination of conventional parts has been effected for purposes of simplicity, their position and function being well known to those familiar with the art.

Prior to the operation of the manually operated switch 86, the valve solenoid 3 is deenergized as contact l is open. Contact 19 is closed, and capacitor is is charged to approximately the full voltage between conductors l and 8 through control grid rectification of tube 22. Contact 28 is, as illustrated, in an open condition thus disconnecting the anode Z l of tube 22 from the conductor l. The contact 34 is closed, thereby shorting out capacitor 33 and the contact 89 is open, no path from secondary 84 through the tube 8| therefore existing. These contacts are mechanically arranged so that the normally closed contacts 19 and 34 will open before the normally open contacts 4, 28 and 89.

Upon closure of the manually operated switch 86, tube 8| will begin to conduct as soon as secondary 84 drives the anode 82 positive with respect to the cathode 33, the conduction of this tube serving to energize the relay coil 81. During the half cycles in which tube 8! does not conduct, due to improper polarity of the transformer secondary 84, the capacitor 88 serves to maintain the relay coil 81 in an energized condition in the conventional manner. As contact l9 opens, the control grid 2! of tube 22 is swept negative with respect to the cathode 23 of that tube due to the charge on capacitor l8. As contact 34 opens, the short across capacitor 33 is eliminated. As the contact 4 then closes, the valve solenoid 3 is energized, and the welding electrodes act to apply pressure to the work in the conventional manner to start the squeeze time period. Closure of contact 28 completes the anode circuit of tube 24, but this tube cannot begin to conduct due to the charge on capacitor l8. Closure of contact 89 forms a non-beat holding circuit across the manually operated switch 8'6.

Tube 22 remains in the quiescent condition aforementioned for a period determined by the timing elements including the capacitor l8 and the resistors in parallel therewith, these elements determining the length of the squeeze time period. The discharge of capacitor 18 through the resistors if; and I1 causes a voltage drop across these resistors which varies with the discharge current. in previous timing systems where short timing periods were desired, the variable resistor would be set to a small value, and the capacitor would discharge through this small value of resistance rapidly. The voltage across the resistor (or resistors) which determined the timing period would therefore rapidly change, and the exact instant at which the timed element, usually an electronic tube, would act at the termination of a timed period would be difiicult to control. This is true especially if the timed element is to be actuated at the end of the timed period by a second voltage, for example a voltage supplied to the shield grid of an electronic tube, as illustrated herein. The circuit illustrated in Figure 1 obviates these difiiculties by using a resistor it having a resistance which is large in comparison with the minimum value of the variable resistance, and by employing as the timing voltage that voltage which is across the resistor ll. As the value of resistance in resistor H is decreased, more and more of the voltage across capacitor it appears across re" sistor ll. Therefore the largest voltage across this variable resistance element at a minimum time setting is relatively small, and as the capacitor l8 discharges current through this element, the actual change in the voltage appearing across it will be relatively small, the greatest part of the voltage of capacitor l8 appearing across resistor [6. The voltage diiierence be tween the cathode 23 and control grid 2| of tube diminished gradually. The shield grid 25 of tube 22 is synchronously driven positive by the pulsating conduction of rectifier I l as it acts to charge the smoothing capacitor [2. One of these positive pulsations of the shield grid, therefore, triggers the tube 22 after the voltage between the grid 2| and cathode 23 is sufliciently small. The resistance of resistor ['6 is suiiiciently small in comparison to the maximum resistance of the variable resistor I! so as to have negligible efiect at that setting.

Prior to the conduction of tube 22, the control grid 4! of the tube 33 is negative with respect to the cathode 3'! of that tube. The capacitor 42 is charged with a polarity according to this voltage difference. As tube 22 begins to conduct, the conductor 35 tends to carry the cathode Ill of the tube 38 a negative amount due to the voltage drop across the adjustable resistor 32, this drop being due to conduction current of the tube 22. This has a tendency to cause the cathode 3'! of tube 38 to become negative with respect to the control grid 4!, but the charge on capacitor 42 momentarily prevents this occurrence. Inasmuch as tube 22, as previously mentioned, is rendered conducting by a positive pulse of voltage upon the shield grid 25 thereof, this positive pulse occurring adjacent to the mid point of a half cycle of voltage, if the capacitor 42 were not present tube 38 might begin to conduct during the latter half of a half cycle, thereby causing current to flow through the ignitrons and the welding transformer for only a portion of a half cycle. Capacitor 42 prevents this unfavorable occurrence, the charge on the capacitor 42 being rapidly dissipated, however, through the resistors 43 and 44 so that during the next positive excursion of anode 39 voltage, tube 38 will conduct to energize the relay coil 41, the conduction therefore occurring only during a whole half cycle.

As current passes from the secondary 46 of transformer through the relay coil 4! and the electronic tube 38, the normally open contact 52 is closed at the instant previously described, causing the conventionally disposed ignitrons 53 and 54 to pass current through the welding transformer 55 for as long as the contact 52 remains closed. During the half cycles of non-conduction of tube 38, the capacitor 68 discharges through the relay coil 41 to maintain the relay in an energized condition. Tube 38 will continue to conduct and the relay coil t! will remain energized for a period determined by the timing combination comprising the adjustable resistor 32 and the capacitor 33. As conduction current of tube 22 passes through the resistor 32 and the capacitor 33 and subsequently through tube 22, a charge is built up upon the capacitor 33 until this charge is sufliciently large to cause the cathode 37 of the tube 38 to become positive with respect to the control grid ll thereof. When this condition prevails, tube 38 is cut oil and no longer conducts. The time required to build a charge on capacitor 33 therefore determines the weld time.

During the first half cycle after tube 33 stops conducting, capacitor 48 will act, as before de scribed, to keep the relay coil 4? energized; during the half cycle following this occurrence, the

inductor 49, which is in series with the capacitor 48, causes a definite deenergization of the relay coil 41, the contact 52 thereby returning to its normal open condition. This opening will not occur until after the trail ignitron has begun to conduct.

During the period in which tube 38 conducts, the primary of transformer 5! is energized, the secondary of the transformer 5| driving the grid 5"; of electronic tube 58 sufl'lciently positive to cause that tube to conduct. This conduction charges capacitor 62 through control grid 66 conduction of electronic tube 67. These pulses occur during the time when th anode 68 of tube t! is negative with respect to the cathode 69 thereof, so that the tube 6'! is immediately cut off by the charge on capacitor 62 and does not, therefore, conduct during the period in which tube 38 conducts.

The timing arrangement comprising capacitor 62 and resistors 59 and SI in the grid circuit of electronic tube 67 is that described earlier and acts to permit the voltage of the cathode and grid to very gradually approach a single value. Superimposed upon the gradually decreasing voltage of capacitor 62 is a synchronizing alternating ripple fed into the voltage divider circuit which comprises resistors 64 and 35 from the transformer secondary el, and, hence, to the control grid 66. This ripple controls the actual moment at which conduction of tube 6! is initiated. Tube 61 will therefore remain non-conductive until capacitor 62 has properly discharged through the circuit in parallel therewith, the actual instant of initiation of conduction being controlled by the positive drive of the synchronizing pulse from the cathode heater circuit. It should be noted that this pulse is applied to the control grid, while the synchronizing pulse applied to trigger tube 22 was applied to the shield grid of that tube.

Throughout the period in which tube 6'! is quiescent, the control grid [2 of tube 13 is at ap proximately the potential of conductor 9 and is intermittently sufiiciently positive so that the tube 73 will. conduct to charge capacitor 76 through control grid [9 conduction of electronic tube 85. Inasmuch as these current pulses occur during the half cycles in which the anode 82 of the tube 8? is positive with respect to the cathode c3 of that tube, tube 8| is not immediately cut ofif, as was the case with tube 6?. Tube 8! will therefore continue to conduct until the before described timing control voltages of tube 5'! are such that that tube 6"! will again resume conduction. The elements which determine these timing voltages thereby control the hold time of the circuit. The conduction of tube El will no longer permit the grid "E2 of tube '53 to become surTiciently positive to permit tube It to conduct, so tr e charge on capacitor 76 cuts oir tube 81 as soon as tube 6'! begins to conduct. The timing circuit controlling conduction of tube Bl is the same as that before described for the control of the tube 57, the voltage between the cathode 83 and control grid 79 being gradually dissipated. As soon as tube 8! is cut off, the relay coil 87 is deenergized and the contacts which it controls are returned to the position indicated in the drawing. Immediately after the circuit controlling the control grid 19 of tube 8i has timed out, the voltage fed into the timing circuit of this tube from the cathode heater secondary 9i triggers the tube 8| which will once again conduct,

provided initiated contact 86 is closed, to initiate another cycle as that herein described.

It will be obvious that the particular circuit arrangement of applicants invention provides an extremely reliable method of timing which is particularly effective in eliminating undesirable loss of control over the timed element during short control settings, especially where a second Voltage is employed to trigger the controlled element. In the illustrated circuit, the electronic tubes are triggered by a ripple voltage supplied to a grid of the tubes employed, and the circuit illustrated clearly shows a plurality of connections to effect this control, the circuit of applicants invention permitting the grid to efiect conduction of the controlled tubes even at minimum time settings.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto, as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

What is claimed is:

1. In a timing system, a capacitor, a source of voltage, means for charging said capacitor from said source of voltage, discharging means associated with said capacitor comprising first and second resistors, said first and second resistors being serially connected and in parallel with said capacitor, said first resistor being fixed while said second resistor is variable, the resistance of said first resistor being small in comparison to the maximum resistance of said second resistor and large in comparison to the minimum resistance of said second resistor, timed means, and means electrically impressing upon said timed means substantially only that portion of the voltage across said discharging means which exists across said variable resistor, whereby said timed means is responsive to voltage drop across said variable resistor and determines a timed period as said capacitor discharges through said fixed and variable resistors.

2. In a timing circuit, a source of voltage, a capacitor, said capacitor being charged from said source of voltage, discharging means for said capacitor comprising serially connected fixed and variable resistors in parallel with said capacitor, the resistance of said fixed resistor being large in comparison with the minimum resistance of said variable resistor, an electronic tube connected across said source of voltage and having an anode and cathode and at least an auxiliary electrode, means for impressing substantially only that portion of the voltage across said discharging means which exists across said variable resistor between an auxiliary electrode and the cathode of said electronic tube as said capacitor discharges through said fixed and variable resistors, and means for superimposing an additional triggering voltage between an auxiliary electrode and said cathode to determine the conduction of said electronic tube to effect a control function.

3. In a timing circuit, a source of voltage, a capacitor, said capacitor being charged from said source of voltage, discharging means for said capacitor comprising serially connected fixed and variable resistors in parallel with said capacitor, the resistance of said fixed resistor being large in comparison with the minimum resistance of said variable resistor, an electronic tube connected across said source of voltage having an anode and cathode and at least a control grid and an auxiliary grid, means for impressing substantially only that portion of the voltage across said discharging means which exists across said variable resistor between the control grid and cathode of said electronic tube as said capacitor discharges through said fixed and variable resistors, and means for superimposing an additional triggering voltage between said auxiliary grid and said cathode to determine the conduction of said electronic tube to efiect a control function.

4. In a timing circuit, a source of voltage, a capacitor, said capacitor being charged from said source of voltage, discharging means for said capacitor comprising serially connected fixed and variable resistors in parallel with said capacitor, the resistance of said fixed resistor being large in comparison with the minimum resistance of said variable resistor, an electronic tube connected across said source of voltage having an anode and cathode and at least a control grid and a shield grid, means for impressing substantially only that portion of the voltage across said discharging means which exists across said variable resistor between the control grid and cathode of said electronic tub-e as said capacitor discharges through said fixed and variable resistors, and means for applying a triggering voltage to said shield grid to determine the conduction of said electronic tube to efiect a control function.

5. In a timing circuit, a source of voltage, a capacitor, said capacitor being charged from said source of voltage, discharging means for said capacitor comprising serially connected fixed and variable resistors in parallel with said capacitor, the resistance of said fixed resistor being large in comparison with the minimum resistance of said variable resistor, an electronic tube connected across said source of voltage having an anode and cathode and at least an auxiliary electrode, means connecting an auxiliary electrode to said capacitor, impedance means connected between said fixed and variable resistors and to the cathode of said electronic tube for impressing the voltage across said variable resistor between an auxiliary electrode and the cathode of said electronic tube, and means for superimposing an additional triggering voltage between an auxiliary electrode and said cathode to determine the conduction of said electronic tube to effect a control function.

6. In a timing circuit, a source of voltage, a capacitor, said capacitor being charged from said source of voltage, discharging means for said capacitor comprising serially connected fixed and variable resistors in parallel with said capacitor, the resistance of said fixed resistor being large with respect to the minimum resistance of said variable resistor, an electronic tube connected across said source of voltage having an anode and cathode and at least an auxiliary electrode, means connecting an auxiliary electrode to said capacitor, resistance means connected across said source of voltage and to said fixed and variable resistors, at least a part of said last mentioned means impressing the voltage across said variable resistor between an auxiliary electrode and the cathode of said electronic tube, and means for superimposing an additional triggering voltage between an auxiliary electrode and said cathode to determine the conduction of said electronic tube to effect a control function.

'7. In a timing circuit, a source of voltage, a capacitor, said capacitor being charged from said source of voltage, discharging means for said capacitor comprising serially connected fixed and variable resistors in parallel with said capacitor, the resistance of said fixed resistor being large in comparison with the minimum resistance of said variable resistor and small in comparison with the maximum resistance of said variable resistor, an electronic tube connected across said source of voltage having an anode and cathode and at least control and auxiliary grids, means for impressing substantially only that portion of the voltage across said discharging means which exists across said variable resistor between the control grid and cathode of said electronic tube as said capacitor discharges through said fixed and variable resistors, and means for superimposing an additional triggering voltage between said auxiliary grid and said cathode to determine the conduction of said electronic tube to efiect a control function.

8. In a timing circuit, a source of voltage, a capacitor, said capacitor being charged from said source of voltage, discharging means for said capacitor comprising fixed and variableresistors 20 in parallel with said capacitor, the resistance of said fixed resistor being large in comparison with the minimum resistance of said variable resistor and small in comparison with the maximum re- 5 auxiliary stantially said discharging means which electrode, means for impressing subonly that portion of the voltage across exists across one of said resistors between an auxiliary electrode and the cathode of said electronic tube as said 10 capacitor variable resistors,

discharges through said fixed and and means for superimposing an additional triggering voltage between an auxiliary electrode the conduction of and said cathode to determine said electronic tube to effect a 15 control function.

References Cited in the file of this patent Number UNITED STATES PATENTS Name Date Few Dec. 17, 1946 Kingsmill June 10, 1947 Solomon May 10, 1949 

